This invention is concerned with a method of forming parisons in the manufacture of hollow articles of glassware, the method comprising forming each parison by introducing a gob of molten glass into a mould cavity having the shape desired for the external surface of the parison, and moving a plunger into the mould cavity to cause the molten glass to conform to the shape of the cavity. The invention is also concerned with a plunger arrangement for use in forming parisons in the manufacture of hollow articles of glassware, the arrangement comprising a plunger, and moving means for moving the plunger into a mould cavity. The invention is also concerned with a plunger for use in such a mould arrangement.
In the formation of parisons in the manufacture of hollow articles of glassware, the parisons are formed in a "blank" mould and the parisons are then transferred to a "finish" mould in which each parison is blown to the shape of the article required. The shape of the mould cavity of the blank mould defines the external shape of the parison. The parison may be blown in the blank mould from a gob of molten glass, in which case the internal shape of the parison is not well defined or, in the well-known press and blow process of manufacturing hollow articles, the parison may be pressed by a plunger which is moved into the mould to press the glass against the mould cavity surface. In this case, the shape of the plunger defines the internal shape of the parison which is, therefore, well-defined. However, when the parison is pressed, although control of the internal shape of the parison is given, it is found that articles produced have damaged internal surfaces so that their strength, particularly their impact resistance, is reduced. It is believed that this damage is produced by contact between the surface of the plunger and the glass during the formation of the parison.
It is an object of the present invention to enable parisons to be formed with well-defined internal shape and without damage to the internal surface of the parison.